Lack of soil disturbance in no‐tillage changes some of the most important basic soil properties. Short‐term changes have been well documented by previous research, but little is known about long‐term changes. This study was to determine the effects of 20 yr of continuous corn (Zea mays L.) under no‐tillage (NT) and conventional moldboard plow tillage (CT) with 0, 84, 168, and 336 kg N ha−1 on soil properties and grain yields and, to the extent possible, compare 20‐yr results with previously published 5‐ and 10‐yr results. Soil organic C and N; extractable P; exchangeable Ca, Mg, and K; and pH were significantly higher with NT than CT in the 0‐ to 5‐cm depth. Below the 5‐cm depth, Mehlich III P; pH; and exchangeable Ca, Mg, and K were higher with CT than NT. Organic C and N increased with increasing N rates. Conversely, pH and exchangeable Ca and Mg declined with high N rates. Bulk density was not significantly different among NT, CT, and bluegrass sod (Poa pratensis L.), but increased with depth. Comparisons of 1989 results with those obtained in 1975 and 1980 revealed that the soil's organic C was restored to the level of the bluegrass sod following a decline of 19% with CT and 9% with NT between 1970 and 1975. Grain yields, which declined along with organic C, have not recovered. Changes in organic matter content, with their many ramifications, are probably the most important long‐term effects of tillage differences on basic soil properties.
The no-tillage cropping system, a combination of ancient and modern agricultural practices, has been rapidly increasing in use. By the year 2000, as much as 65 percent of the acreage of crops grown in the United States may be grown by the no-tillage practice. Soil erosion, the major source of pollutants in rural streams, is virtually eliminated when no-tillage agriculture is practiced. The no-tillage system reduces the energy input into corn and soybean production by 7 and 18 percent, respectively, when compared to the conventional tillage system of moldboard plowing followed by disking. In addition, crop yields are as high as or higher than those obtained with traditional tillage practices on large areas of agricultural land.
Many of the advantages of no-tillage crop production are due to the presence of a mulch from a cover crop or from crop residue. Legumes can be used to provide the mulch and biologically fixed N to nonlegumes in the system. Field experiments were conducted from 1977 through 1981 to determine the amount of biologically fixed N provided to no-tillage corn (Zea mays L.) by winter annual legume cover crops of hairy vetch ( Yicia villosa Roth), big flower vetch ( Yicia grandiflora W. Koch var. Kitailbeliana), and crimson clover (Trifolium incarnatum L.). The legumes were compared to a co,ver of corn residue only and a cover crop of rye (Secale cereale L.). The soil was a Maury silt loam (Typic Paleudalfs, fine-silty, mixed, mesic). Fertilizer N treatments of 0, 50, and 100 kg ha·• were combined with each cover treatment. Corn was planted by no-tillage directly into the cover treatments and the cover crops were killed with herbicides. Hairy vetch produced more dry matter with a higher N percentage which resulted in a higher N concentration in corn plants and substantially more inorganic N (KCI extractable NHt and
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